The present invention generally relates to devices and methods for completing oil and gas wells, and more specifically to a method and apparatus which provides an economic and relatively simple means of sealing the top of a liner within a casing string.
It is well known to those in the oil and gas industry to complete oil and gas wells with a liner across the production interval of the well. The liner might be set in an xe2x80x9copen holexe2x80x9d section at the bottom of the well or the liner might be set within a cased section of the well. In either case, when the liner is placed within the well, an annulus is created. The annulus comprises the planar surface defined by the space between the outside wall of the liner and, depending upon whether the liner is set in open hole or in a cased section of the well, either the inside diameter of the casing, or the diameter of the open hole. Generally, the top of the liner extends upwardly such that the top of the liner is within a cased section of the well.
It is often desirable or required that the annular space between the top of the liner and the inside diameter of the casing be scaled so as to prevent flow of reservoir fluids or completion materials around the top of the liner into the casing above the liner. Various means are known within the oil and gas industry for sealing the top of the liner, which include placing a cement seal in the annular space, having a seal element between the top of the liner and the inside wall of the casing, or driving a moldable material, such as lead, over the top of the liner. The type of seal will often be dictated by the operational requirements for the well, including the required pressure and temperature ratings.
Gravel packing operations are one example where it is usually desirable to seal off the top of the liner to prevent flow of reservoir fluids and/or to prevent gravel from migrating around the top of the liner. Gravel packing is used to control the flow of reservoir sand into the well bore by circulating gravel into the well, such that the gravel is placed between the liner (or sand screen) and the producing formation.
In one form of gravel packing, the liner is run into the well on a tool string until the liner rests on the bottom of the well. At the top of the liner is a landing nipple which is connected to the tool string. A gravel slurry is then pumped down the tool string and around the liner. After the gravel slurry is in place between the liner and the producing formation, the tool string is removed, leaving the top of the liner facing upwardly within the casing. A drive-over adapter is thereafter run into the well on a work string, where the drive-over adapter is driven over the top of the liner to form a seal between the outside diameter of the top of the liner and the inside diameter of the casing. While this method provides a relatively inexpensive well completion, it nevertheless requires additional rig time to make a second trip with the work string to run in the drive-over adapter.
The present invention is directed to an apparatus and method for sealing the top of a liner within a casing string of an oil well which does not require a second trip of the work string to seal off the top of the liner within the casing. The liner, connected to the apparatus, is run into the well on a work string until the bottom of the liner sets on the bottom of the well. After the bottom of the liner is set on the bottom of the well and, if desired, a gravel slurry is circulated into place, the apparatus is actuated by setting weight on the work string, which causes a cylindrical sealing element to expand and seal against the inside wall of the casing.
One embodiment of the apparatus comprises a hollow cylindrical mandrel having an inside surface, an exterior surface, a first end and a second end. The first end and second end define a longitudinal axis, the first end having a first set of internal threads adapted to engage the threads of a run-in tool and the second end adapted to connect to the top of the liner. The exterior surface comprises a wicker section having a plurality of first wicker members disposed circumferentially about the mandrel. The mandrel further comprises a plurality of slots extending from the inside surface to the exterior surface, each slot having a major axis coincidental with the longitudinal axis. An outer cylindrical housing, a cylindrical lock ring, a cylindrical sealing element, and a cylindrical slip ring, are slidably disposed over the exterior surface of the mandrel along the longitudinal axis in relative order, the lock ring adjacent to the wicker section of the mandrel. The outer cylindrical housing further comprises a top end which is adjacent to the first end of the mandrel, the top end having a second set of internal threads adapted to engage the threads of the run-in tool when the run-in tool is disengaged from the first set of internal threads. The cylindrical housing further comprises a plurality of tapped holes extending through the wall of the housing, each hole configured to overlay one of the slots of the mandrel. The lock ring comprises an inside surface having a plurality of second wicker members adapted to engage one or more of the first wicker members of the mandrel. The apparatus further comprises a plurality of lugs for insertion into the holes of the cylindrical housing, each lug extending into the slot which coincides with the hole. Each lug has a head and a body section, the body section being threaded to be received by the tapped hole, each lug having a length such that the body section extends into the slot but does not penetrate beyond the interior surface of the mandrel, such that the inside diameter of the mandrel is not restricted by the lugs.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.